Shield for mercury vapor lamps



Jan. 2, 1945. J. A. ROBERTS SHIELD F OR MERCURY VAPOR LAMPS Filed Feb.14, 1942 m mm M WA M m Patented Jan. 2, 1945 SHIELD FOR MERCURY VAPORLAMPS John A. Roberts, New York, N. Y., assignor of onehalf to H. DorseySpencer, New York, N. Y.

Application February 14, 1942, Serial No. 430,939

4 Claims.

This invention relates to devices for improving both the efllciency andthe light values of various illuminating devices, and particularly thosein which mercury vapor is employed.

The efliciency of mercury vapor lamps, and

mercury vapor is employed to produce the ultraviolet radiation whichactivates the fluorescent lining of the lamp tube, is affectedconsiderablyby changes in temperature of the tube or bulb wall of thelamp. For highest efliciency it has been found that the bulb walltemperature of fluorescent lamps should be stabilized within the rangeof from 100* to 120 F. and that marked variations from this range willcause a sharp drop in rescent light has been produced by a newer lampcalled "soft white," but even the purpose of this lamp has been largelydefeated by its bad color particularly of those fluorescent lamps inwhich distortion.

A simple and inexpensive solution of the problem caused by excessivecoldness of fluorescent daylight is, therefore, an incidental object ofthe light efllciency. This drop in efllciency is dueto (a) Condensationof mercury vapor within the lamp at lower temperatures, and V (b)Increased vapor pressure at'higher temperatures. t

One of the objects of the presehtimieffiion is to improve the overallefllciency of mercury vapor lamps, and particularly of mercury vaporlamps of the fluorescent type, by preventing marked variations in thebulb wall temperature. Fluorescent lighting is rapidly replacing otherforms of artificial illumination because of its economy of operation andbecause it provides a whiter and more optically efficient light than thelight produced from a tungsten filament. Fluorescent illumination asthus far developed has, however, certain peculiarities and objectionablecharacteristics which it is the purpose of the present invention toovercome in a simple and inexpensive way.

The sensitiveness of the mercury vapor and fluorescent lamps totemperature changes and particularly to drafts has been referred tohereinabove and, as above suggested, the principal object of the presentinvention is to protect such lamps from marked variations in the bulbwall temperature and thus maintain a high efficiency of operation.However, one of the objectionable characteristics of fluorescentillumination, as it has so far been developed, is that the light fromwhat is called the fluorescent daylight lamp is admittedly a very coldappearing light, generally too cold to be acceptable for use in the homeor in other places where true daylight color values are not the primaryobject. To offset this objection, fluorescent lamp manufacturer havemodified the so-called daylight" lamp by producing another lampdesignated as white. This lamp has also proved to be still unpleasantlycold and, therefore, more recently a still warmer fluo- .presentinvention.

the invention aims to provide a simple and comaratively inexpensivecombined temperature stabilizing shield and light filter, preferably inthe form of a sheath which can be slipped over the lamp tube and whichwill serve both to protect the tube against marked changes in the bulbwall temperature and also, where desired, to produce the desired lightcorrection or color effect.

an important feature of the invention is the provision of a lightweight, inexpensive and easily applied combined temperature stabilizingcovering for tubular lamps, and particularly :for fluorescent lamps,which is formed of translucent elastic sheet material so conformed tothe lamp tube with which it is to be used as to be selfsupporting whenin temperature stabilizing relation thereto and yet having the greaterpart of its surface so spaced from the lamp tube as to provideventilation and thus overheating. A further important feature of theinvention is the formation of the greater part of the sheath or shieldor fluted elastic material so conformed to the lamp tube that the ridgesof the flutes will engage the tube and assist in maintaining the sheathin proper relation thereto. Among the advantages of this last-mentionedconstruction are the provision of passages for ventilating air betweenthe greater part of the sheath or shield and the tube and the fact thatonly a very small part of the surface of the sheath or shield isactually in contact with the tube. Overheating of thetube is thusprevented by the moderate circulation of the combined insulating andheat removing air between the sheath and the tube and overheating of thesheath or shield is also prevented by the relatively small amount ofsurface of the sheath or'shield brought into heat-conducting contactwith the lamp tube.

Other objects and important featuresof the invention will appear fromthe following descrip tion and claims when considered in connection withthe accompanying drawing, in which Figure 2 is a transverse sectionthrough the structure shown in Figure 1;

Figure 3 shows a slightly modified form of the sheath illustrated inFigures 1 and 2, the modification being designed to adapt the sheath foruse'with fluorescent lamps in which the lamp tube is located close tothe reflector;

Figure 4 is a modified form of the sheath for use with the ordinarycylindrical fluorescent lamp tube;

Figure 5 shows still another modification of the sheath suitable forvuse with cylindrical fluorescent lamp tubes;

Figure 6 shows a slight modification of the sheath construction shown inFigure 5, and

Figure '7 shows a modification of the fluorescent lamp tube section topermit the use of a cylindrical form of sheath without spacing ribs orlugs.

In the illustrative embodiment of the invention shown in Figures 1 and2, the fixture which supports the fluorescent lamp tube 2 comprises endsockets. and 6 for thetube; said sockets being carried upon a reflectorstructure 8 supported from the ceiling, or other suitable part of theroom to be illuminated, by hollow rods iii and I2 through which theelectrical connections to the lamp are made. ihe sheath i4 shown inFigures 1 and 2 is made of translucent elastic plastic sheet material,preferably having a very low coemcient of light absorption, and thissheet material is pleated, preferably to form longitudinal flutes. Asherein shown, the longitudinal flutes of the sheath ware iormed withcomparatively sharp ridges, but it will be understood that the inventionis not restricted to the particular flute shape here shown or to acomparatively large number of flutes shown and that,

any other form of flute which will provide channels It for insulatingand ventilating purposes may be employed. One advantage of thecomparatively sharp ridges showninthe illustrated sheath M isthat theamount 0! the surface of the sheath l4 that is brought-into actualcontact with the tube 2, even with the large number of flutes shown, iscomparatively slight thus preventing much conduction of heat directlyfrom the tube 2 to the sheath ll.

When a fluted sheath, such as shown in Figures 1 and 2, is to be usedwith a fixture in which the tube is located in close proximity to thereflector, as, for example, in the structure shown in Figure, 3 in whichthe curved reflector I8 is spaced only a short distance from the uppersurface of the tube 2, the fluting maybe omitted from that part of thesheath which is to cover the part of the tube 2 closest to the reflectorit, this partof the sheath, asshown, being formed of smooth overlappingmargins and 22, preferably cemented together to complete the tubularform of the sheath. I

It will be seen that a sheath such as shown in Figures 1, 2 and 3, whichis made up of translucent elastic plastic sheet material, pleated intolongitudinal flutes asshown, will, when formed into a complete tube,adjust itselfreadily to fluorescent lamp tubes of slightlydlfierent'diameters and that it will provide insulation for the lamptube against sharp changes in the temperature of the surroundingatmosphere, and particularly against draughts, by reason of the airwhich is in the channels it and that-these channels 16 will also providefor a moderate circulation of air therethrough to carry away any excessheat.

that might tend to accumulate by reason of the insulation thus provided,thereby preventing overheating of the tubes.

In Figure 4 is shown a modified embodiment of the invention which willprovide ventilation to prevent overheating of the tube but which mayrequire a somewhat thicker plastic sheet to give the same degree ofinsulation, by reason of the lackof the closely spaced air channels l6and by reason of the more extensive contact of the surface of theplastic with, the lamp tube. As shown in Figure 4, the sheath 24 isoctagonal in form thus providing air channels 26. This sheath 24, likethe sheath I 4, allows for some variation in the diameterbf the tube 2.such variation, if on the high side, causing a distor-" tion of theoctagonal form or, in other words, a

, as continuous ribs, the sheath maybe formed as a continuously.extruded tube of the plastic of the sectional shape shown in Figure 5,thus avoiding the necessity for cementing together the overlapping orabutting margins of the sheet, as is done in the forms shown in Figures2, 3, 4 and '7.

Byso proportioning the diameter of the sheath 28 to the diameter of thelamp tube 2 with which it is to be used that, when the sheath iseccentrically positioned on the lamp tube, as shown in Figure 5, theventilating and insulating space 32 will be sufiicient to maintain thedesired tube temperatures, then the fact that the part of the sheathadjacent to the reflector, that is, the part covering the top part ofthelamp tube 2 is in immediate contact with the tube will not materiallyaifect-the desired overall result.

In the form of the invention shown in Figure 6,

which is a modification of the structure shown in Figure 5, the sheath34 is shown, not as a complete tube completely surrounding the lamp tube2, but as an elastic structure, open on the top side where the tube ismore or less protected by the reflector of the fixture anyway, thiconstruction having the advantage that it maybe sprung over the lamptube '2 without removing it from its fixture." It will be understoodthat this provision of an open side is not restricted to this form ofthe invention and that, if the plastic employed in making the sheath besufiiciently elastic to form a self-sustaining sheath shape.

any form of the sheath of the present invention Figure '7 is madepolygonal in cross section, the

illustrated lamp tube being shown a hexagonal in section. This permitsthe use of a cylindrical sheath 38 of a diameter which permits it toengage each of the apices of the angles of the hexagon. As will be seen,the curvatureof the sheath 38 away from the plane sides of the hexagon36 provides the insulating and ventilating passages 40 between thesheath 38 and the tube 36.

From the foregoing description it will be seen that the presentinvention provides simple and comparatively inexpensive means forincreasing invention, because of its comparatively low absorption oflight and because of its high resistance to deterioration when subjectedto the lamp heat and other conditions which are met with in the use ofsheaths of the present invention with fluorescent lamps, is the plasticsold under the trade name 01 Plastacele.- Another plastic that has givenvery satisfactory results in use in sheaths embodying thepresentinvention is one sold under the trade name of Lumarith.

be seen that, by reason of the ease with which it can be given anydesired color, tint or shade, it lends itself readily both to colorcorrection,

where necessary, and to the production of color eflfects in lighting,as, for example, in store window displays.

What is claimed as new is: -1. A temperature stabilizing covering fortubular lamps of the mercury vapor type comprising translucent elasticsheet material of substantially uniform thickness and sufficientlyconformed to the shape of the lamp to be self-supporting thereon whenbrought into protective relation thereto, said covering enclosing alllight radiating parts of the lamp tube which would otherwise be'directlyexposed to atmospheric changes in the illuminated sp'ace and havinglamp-engaging por- When Plastacele is employed as the plastic for use inmaking the sheath of the present invention, a colorless sheet of thisplastic of the thickness required to give the desired elasticity andstrength and shaped to form a sheath such as shown in Figures 1, 2 and 3is estimated to have a light absorption factor of about 2%. If,therefore, a sheath of the form shown in Figures 1, 2 and 3 beconstructed of colorless Plastacele of the aforementioned thickness andbe used with a fluorescent lamp subjected to considerable variations intemperature of the surrounding atmosphere, it will be found that thelight output of the lamp at low temperatures will be markedly increasedand that there will be substantially no lowering of the output ascompared with a bare lamp until the temperature of the surrounding airpasses normal room temperature. It will thus be seen that for usuallighting conditions the use of the sheath of the present invention willincrease the overall efiiciency of the fluorescent lamp and that onlyunder abnormal conditions, that is, when the atmosphere surrounding thelamp is above normal room temperature will there be loss of emciency ascompared with the bare.

tions thereof so construe ed and arranged that the major portion of theinner surface of said sheet material is only slightly spaced from the alamp when in protective relation thereto but is provided with continuouslongitudinally extending open-ended air channels between said lamp andsaid protective covering which serve not only for containing-insulatingair but also for permit 7 ting heat-removing circulation thereofsuflicient out the greater portion of its tube covering area and is soconformed to the lamp tube with which it is to be used that, when thecovering is in protective relation thereto, ridges of the flutes engage.2 the tube throughout its light radiating extent "and form ventilatingand insulating channels continuous from end to end thereof.

- 3. A temperature stabilizing covering according to claim 1 in whichthe elastic sheet material is moulded into a tube, the adjacent marginsof the sheet being left unconnected whereby the tube may be sprung intocovering position on the lamp. 7

v 4. A temperature stabilizing covering according to claim 1 in whichthe translucent sheet material is composed of a translucent plasticwhich,

when uncolored and of a thickness sufficient to provide the requiredself supporting elastic in the finished structure, has a lightabsorption coeflicient of only about two per cent of the rays passingdirectly therethrough.

JOHN A. ROBERTS.

